(CNN) -- Officials declared a state of emergency Saturday after a powerful predawn earthquake struck near Christchurch, New Zealand, sending people into the streets as windows exploded, water mains broke and buildings crumbled.

No deaths were immediately reported.

The Christchurch City Council declared a state of emergency in response to what it called "significant damage," just hours after the 7.0-magnitude earthquake rattled residents. The order allows authorities to force evacuations and prohibit entry into areas believed unsafe. Officials in Selwyn, a rural district near where the quake hit, also declared a state of local emergency.

A curfew from 7 p.m. to 7 a.m. was in place, and the army was assisting local police to ensure there is no looting.

Roughly 100 people were being treated for minor bumps and cuts after the strong quake, hospital officials said. Two people suffered more serious injuries.

"The house felt like it was on wheels, like it was rolling around on marbles," resident Hadlee Wright told CNN's Rick Sanchez.

Pictures that Wright took of the city before daybreak showed collapsed buildings and streets littered with bits of brick and rock. The facade of one structure was almost entirely torn off.

Power was out in the northwest part of the city, while water and sewage services have been affected in several regions, the Christchurch Civil Defense Group said in a statement. Roads also were damaged.

Images taken by Jimmy Le Comte, and sent to CNN's iReport, showed flooding in New Brighton, a Christchurch suburb. In one, a giant crack cuts across a road.

The quake had a magnitude of 7.0, down from an initial assessment of 7.4, the U.S. Geological Survey said. It struck about 35 miles from Christchurch, a city with a population of some 386,000 people on the east coast of South Island.

An aftershock with a magnitude of 5.7 struck not far from the epicenter about 20 minutes later, the survey said.

A man in his 50s was hit by a falling chimney, while another suffered serious injuries after being cut by glass, said Michele Hider, a spokeswoman with Christchurch Hospital.

Sebastian Koga, a hospital neurosurgeon, said roughly 100 people were being treated for minor injuries. He was not aware of any deaths.

"We've had a flood of lacerations and minor head injuries, but nothing that could not be handled," Koga said.

Civil Defense Minister John Carter said the country's prime minister is headed to Christchurch to assess the earthquake damage.

"We don't know entirely what level of issues we're dealing with at the moment. We're still getting reports on it, but it has been extensive," Carter told CNN affiliate TVNZ. "We were lucky that the impact on the people from a death point of view has not been what it could have been under normal circumstances."

The earthquake struck at 4:35 a.m. Saturday (12:35 p.m. ET Friday), when few people would have been out and about. Police said there was some initial looting activity, but that it was quickly brought under control.

A man who was at the international airport in Christchurch described the scene.

"The entire terminal started shaking," he said. "I knew it was an earthquake. There was not much you could do at that point."

Authorities evacuated the airport, he said, adding that he saw minor damage.

Reinier Eulink, general manager of the Holiday Inn in Christchurch, said there is damage around the hotel corridors and "big cracks in the walls."

"It was a big big long jolt, and the building moved a lot," he said. The 13-floor building, with about 150 rooms, was about 40 percent occupied, and he estimated that 80 or more people were staying at the hotel at the time.

Power was knocked out, but emergency power came on, Eulink added. People were milling around in the hotel lobby, trying to get warm during the chilly Southern Hemisphere winter.

The quake was 7.5 miles deep, according to the U.S. Geological Survey. The Pacific Tsunami Warning Center said the event is not likely to generate a tsunami.

Prime Minister John Key told CNN affiliate TVNZ it would likely be some time before the full cost of the quake could be calculated. He sought to reassure residents.

"We're not going to let Christchurch suffer this great tragedy on its own," said Key.